It is known from DE-GM No. 17 67 158 that curlers of foam, or "rollers", can be formed with a longitudinal bore and that a stabilizing wire, which is also used to receive a clip for a curl of hair to be held on the curler, can be introduced into the bore. The wire may be flexible or elastic, uncoated or plastic-coated. Also, it may be freely moved back and forth in the bore and projects therefrom at both ends to such an extent that a clip for a curl of hair may be fastened thereto. The curlers according to DE-GM No. 17 67 158 are relatively stiff and cannot be compared in terms of function and cost with the roller-type hair curlers which are the subject of this invention.
In addition DE-GM No. 16 77 386 and DE-GM No. 16 97 640 disclose curlers having wire inserts which are shorter than the length of the curler. In DE-GM No. 16 77 386 a plastic foam is cast in the mold of the desired hair curler with a wire insert therein. In DE-GM No. 16 97 640 a locking curler of foam rubber is disclosed containing a metal insert. No method is described for the manufacture of the curler.
In the past, hair rollers have been produced by in-mold foaming. To this end, an extrusion-foamed granulate consisting, for example, of low-density polyethylene (LDPE) or of polyurethane (PUR) is produced and subsequently processed to form the molding. The extrusion die used for this purpose is for example, a breaker plate. The foamed strands are size-reduced immediately after issuance from the die to form the granulate. The granulate is introduced into the particular mold, optionally after radiation-induced cross-linking to gel contents of from about 20 to 40%, and heated until it melts at the surface by heating of the mold. By subsequent reduction of the volume of the mold, the hot granulates are consolidated to form a molding. If the roller-type curlers individually mold-foamed in this way are to be sufficiently stable, a length of wire has to be introduced, generally by hand, into their cores.
Roller-type curlers produced by in-mold foaming have an undesirably high specific gravity for practical application. Accordingly, hair curlers having unit weights below 100 kg/m.sup.3 have been produced by extrusion foaming. Unfortunately, curlers such as these do not have the necessary stability for practical application because the pieces of wire separately introduced during in-mold foaming to stabilize the curler could not be integrated into the production process in extrusion foaming when they have to be shorter than the foam body.